feat: Add complete user authentication system

[kris70lesgo]

🚀 Pull Request

📋 Description

This PR implements a comprehensive user authentication system for SmartLog, enabling individual users to create accounts and securely access their personal expense tracking data.

Key Features Added:

• User Registration: Complete signup flow with form validation
• User Login: Secure authentication with JWT tokens
• Protected Routes: Dashboard and expense tracking features now require authentication
• Password Security: Bcrypt hashing with salt rounds
• Token Management: Access/refresh token system with HTTP-only cookies
• Persistent Login: Users stay logged in across browser sessions
• Error Handling: Comprehensive validation and user feedback
• Loading States: Improved UX with loading indicators

Fixes #189

🔍 Type of Change
New feature ✨

Refactoring or code improvement ♻️
Other (please describe):

🙋 Your Details
Name: Agastya khati
Email ID: krishkhati70@gmail.com

🧪 How Has This Been Tested?
Backend Testing:

✅ User registration API endpoint (POST /api/v1/users/sign-up)
✅ User login API endpoint (POST /api/v1/users/sign-in)
✅ User logout API endpoint (POST /api/v1/users/logout)
✅ JWT token generation and validation
✅ Password hashing and verification
✅ Protected route middleware functionality

Frontend Testing:

✅ Registration form with validation (password matching, required fields)
✅ Login form with loading states and error handling
✅ Protected route redirection (unauthenticated users redirected to login)
✅ Authentication context state management
✅ Persistent login across page refreshes
✅ Logout functionality clearing user session
✅ Toast notifications for user feedback

Integration Testing:
✅ Complete user journey: Register → Login → Access Dashboard → Logout
✅ Authentication persistence across browser tabs
✅ Proper error handling for invalid credentials
✅ Form validation and user feedback

[vercel]

@kris70lesgo is attempting to deploy a commit to the Tanmay Kalra's projects Team on Vercel.

A member of the Team first needs to authorize it.

[kris70lesgo]

@TanmayKalra09 can u review it ?